Controlling and switching the chiroptical properties of (macro)molecules is of continued interest because of potential applications in sensor data storage, optical devices, and liquid crystalline displays. Chiroptical switch can be controlled by temperature (Bradbury, E. M. et al. Biopolymers 1968, 6, 837; Watanabe, J. et al. Macromolecules 1996, 29, 7084; Maeda, K.; Okamoto, Y. Macromolecules 1999, 32, 974; Cheon, K. S. et al. Angew. Chem., Int. Ed. 2000, 39, 1482; Tang, K. et al J. Am. Chem. Soc. 2003, 125, 7313; Fujiki, M. J. Am. Chem. Soc. 2000, 122, 3336; Fujiki, M. et al. A. Silicon Chem. 2002, 1, 67; Fujiki, M. et al. J. Am. Chem. Soc. 2001, 123, 6253; Teramoto, A. et al. J. Am. Chem. Soc. 2001, 123, 12303; Tabei, J. et al. Macromolecules 2004, 37, 1175; Cheuk, K. K. L. et al. Macromolecules 2003, 36, 9752; Nakako, H. et al. Macromolecules 2001, 34, 1496; Tabei, J. et al. Macromolecules 2003, 36, 573; Yashima, E. et al. J. Am. Chem. Soc. 2001, 123, 8159), solvent (Khatri, C. A. et al. J. Am. Chem. Soc. 1997, 119, 6991; Bradbury, E. et al. Macromolecules 1971, 4, 557; Toniolo, C. et al. Biopolymers 1968, 6, 1579), additives (Novak, B. M.; Schlitzer, D. S. J. Am. Chem. Soc. 1998, 120, 2196; Yashima, E. et al. Nature 1999, 399, 449; Ishikawa, M. et al. J. Am. Chem. Soc. 2004, 126, 732; Miyake, H. et al. J. Am. Chem. Soc. 2004, 126, 6524; Su, S.-J. et al. Macromolecules 2002, 35, 5752; Berl, V. et al. Nature 2000, 407, 720), irradiation (Koumura, N. et al. Nature 1999, 401, 152; Huck, N. P. M. et al. Science 1996, 273, 1686; Janicki, S. Z.; Schuster, G. B. J. Am. Chem. Soc. 1995, 117, 8524; Mayer, S. et al. Macromolecules 1998, 31, 8522; Muller, M.; Zentel, R. Macromolecules 1994, 27, 4404; Maxein, G.; Zentel, R. Macromolecules 1995, 28, 8438; Muller, M.; R. Zentel Macromolecules 1996, 29, 1609; Mayer, S.; Zentel, R. Macromol. Chem. Phys. 1998, 199, 1675) and electron redox (Zahn, S.; Canary, J. W. Science 2000, 288, 1404; Zahn, S.; Canary, J. W. Trends Biotechnol. 2001, 19, 251), with thermo-driven chiroptical switching polymers being the most extensively studied. Examples include poly(L-aspartate β-esters) (Bradbury, E. M. et al, Biopolymers 1968, 6, 837; Watanabe, J. et al., Macromolecules 1996, 29, 7084), polyisocyanates (Maeda, K.; Okamoto, Y. Macromolecules 1999, 32, 974; Tang, K. et al. J. Am. Chem. Soc. 2003, 125, 7313), polysilanes, (Fujiki, M. J. Organomet. Chem. 2003, 685, 15; Fujiki, M. J. Am. Chem. Soc. 2000, 122, 3336; Fujiki, M. et al. Silicon Chem. 2002, 1, 67; Fujiki, M. et al. J. Am. Chem. Soc. 2001, 123, 6253; Teramoto, A. et al. J. Am. Chem. Soc. 2001, 123, 12303) and polyacetylenes (Tabei, J. et al. Macromolecules 2004, 37, 1175; Cheuk, K. K. L. et al. Macromolecules 2003, 36, 9752; Nakako, H. et al. Macromolecules 2001, 34, 1496; Tabei, J.; Nomura, R.; Masuda, T. Macromolecules 2003, 36, 573). Solvent-driven chiroptical switching has been reported for poly(L-aspartate β-esters) (Bradbury, E. M. et al., Biopolymers 1968, 6, 837; Bradbury, E. M. et al. Macromolecules 1971, 4, 557; Toniolo, C. et al. Biopolymers 1968, 6, 1579) and poly(propiolic esters) (Nakako, H. et al. Macromolecules 2001, 34, 1496).
To date, however, all chiroptical switching polymers are synthesized from chiral monomers, possessing stereo centers in the main or side chains. Herein, we wish to report the first chiroptical switching polymer (poly[N-(1-anthryl)-N′-octadecylguanidine], poly-1b, see Scheme 2), which possesses no chiral moieties in polymer chains. Poly-1b is synthesized by a highly regioregular, stereoregular, helix-sense-selective polymerization.
The helix-sense-selective polymerization of achiral monomers using chiral catalysts or chiral solvents yields kinetically controlled helical polymers, e.g., polyisocyanides (Deming, T. J.; Novak, B. M. J. Am. Chem. Soc. 1992, 114, 7926; Nolte, R. J. M. et al. J. Am. Chem. Soc. 1974, 96, 5932; Kamer, P. C. J. et al. J. Am. Chem. Soc. 1988, 110, 6818), poly(quinoxaline-2,3-diyl)s, (Ito, Y et al., Macromolecules 1998, 31, 1697; Ito, Y et al., Chem., Int. Ed. Engl. 1992, 31, 1509), poly(trityl methacrylates) (Okamoto, Y.; Nakano, T. Chem. Rev. 1994, 94, 349; Nakano, T.; Okamoto, Y. Macromolecules 1999, 32, 2391; Okamoto, Y. et al. J. Am. Chem. Soc. 1979, 101, 4763; Nakano, T. et al. J. Am. Chem. Soc. 1992, 114, 1318), poly(trityl methacylamides) (Hoshikawa, N. et al. J. Am. Chem. Soc. 2003, 125, 12380), polyacetylenes, (Aoki, T. et al. J. Am. Chem. Soc. 2003, 125, 6346), and polyisocyanates (Okamoto, Y. et al. Polym. J. 1993, 25, 391).
Recently, we reported our preliminary results on the helix-sense-selective polymerization of achiral carbodiimides using [(R)- and/or (S)-binaphthoxy](diisopropoxy)titanium(IV), R-1 and/or S-1, catalysts (Scheme 1) (Tang, H.-Z. et al. J. Am. Chem. Soc. 2004, 126, 3722; Tian, G. et al. J. Am. Chem. Soc. 2004, 126, 4082). However, the helical polyguanidines obtained possess regioirregular backbones. We concluded that it is resulted from the multiple catalytically active species, such as monomer, dimers, and trimers of titanium complexes. (Boyle, T. J. et al. Organometallics 1992, 11, 1112; Balsells, J. et al. J. Am. Chem. Soc. 2002, 124, 10336; Davis, et al. Org. Lett. 2001, 3, 699; Pescitelli, G. et al. Organomettallics 2004, 23, 4223). To precisely control the regioselectivity in the polymerization of unsymmetrical carbodiimides, structurally well-defined monomeric titanium catalysts are required. However, to date, monomeric titanium alkoxide complexes are few in number.